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Head and Neck > Anatomy of the eye and orbit > Flashcards

Anatomy of the eye and orbit Flashcards

1
Q

what are the three layers of the eyeball?

A

Fibrous coat
Vascular coat
Sensory coat

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2
Q

what does the fibrous coat of the eye contain?

A

collagen, complete layer or a complete coat that envelops the entire globe

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3
Q

how much of the eye does the vascular coat cover?

A

goes all the way through except at the very anterior region, where it’s slightly deficient and you’ve got the opening of the pupil

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4
Q

how much of the eye does the sensory coat cover?

A

extends only just anterior to the equator off the eyeball

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5
Q

what comes off of the posterior aspect of the eyeball?

A

Then going out from the posterior aspect of the eyeball is cranial nerve number 2, or the optic nerve.

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6
Q

what two structures make up the fibrous coat?

A

The sclera, which is nothing but the white of the eye, which forms the posterior five sixths of the eyeball.

And most anteriorly sitting, like a watch glass, is the anterior one sixth that is transparent and it’s called as the cornea.

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7
Q

hoe much of the eyeball does the sclaera cover?

A

which is nothing but the white of the eye, which forms the posterior five sixths of the eyeball

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8
Q

how much of the eyeball does the cornea cover?

A

most anteriorly sitting, like a watch glass, is the anterior one sixth that is transparent

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9
Q

what are the three parts of the vascular coat?

A

iris, which is what you can see through the cornea and gives you the colour of the eye.
As we mentioned before, it is deficient most anteriorly in this opening called as the pupil.

Behind the iris, you have the ciliary body. And then posterior to that you have this vascular structure called as the choroid.

So three parts make up the vascular layer: The iris, the ciliary body, and the choroid.

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10
Q

what is the sensory coat made up of?

A

made up of the retina

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11
Q

what does the retina end in?

A

the retina ends in a very serrated margin - ora serrata

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12
Q

what are both the sclera and cornea made up of?

A

collagen

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13
Q

how is the collagen within the sclera arranged?

A

collagen fibres of different diameters arranged quite irregularly that give it the white opaque appearance.

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14
Q

how is the collagen within the cornea arranged?

A

very fine uniform, collagen fibres, which allow light to pass through it, and therefore it is transparent.

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15
Q

what is the function of the iris, and what does it contain to do this?

A

iris controls the diameter of the pupil, within it are a series of circular and radial muscles that help it to control the diameter of the pupil

enable the right amount of light from entering into the eyeball.

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16
Q

what are the two functions of the ciliary body?

A

Firstly, from it are little spidery web-like zonules or suspensory ligaments that help to suspend the crystalline

Secondly, it produces a fluid called as the aqueous humor, and this aqueous humor fills all of the space in front of the lens.

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17
Q

which part of the choroid is richly vascular?

A

The choroid at the back is richly vascular and its main function is to supply the outer layers of the retina with blood.

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18
Q

what does the retina contain?

A

The retina is the neural or the sensitive layer.
It has within it a number of neurones, including modified neurones called as the rods and cones.

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19
Q

what is the crystalline lens suspended from?

A

can change its shape and help to focus light rays on the retina - suspended from the ciliary body

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20
Q

what is the space infront of the crystalline lens known as?

A

anterior segment of the eye, and it’s filled by a watery fluid called as the aqueous humor which in turn is secreted by the ciliary body

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21
Q

what is the space behind the crystalline lens known as?

A

The space behind the lens,
this larger space just here, is called as the posterior segment.
And in the posterior segment, you have a gel called as the vitreous humor.

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22
Q

what is the function of the vitreous humour?

A

And this gel helps to tamponade or push the retina back against the choroid.

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23
Q

what is the aqueous humour?

A

The aqueous humor is watery and it’s secreted by this structure here, which is the ciliary body - It flows and and completely fills the anterior segment of the eye.
then it gets reabsorbed back into the systemic circulation.constant production of aqueous humor by the ciliary body, a constant circulation and a constant of reabsorption cycle helps to maintain intra-ocular pressure

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24
Q

what is the vitreous humour?

A

less of a secretion and reabsorption, there’s almost none of that
But the water in the vitreous humor keeps getting replenished.
its main job is to push the retina back against the choroid and prevent it from getting detached

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25
Q

label the different parts of the eye?

A
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26
Q

function of the ciliary body?

A

Suspends the lens and produces Aqueous Humor

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27
Q

function of the iris?

A

Controls the diameter of the pupil and thereby controls the amount of light rays entering the eyeball

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28
Q

function of the choroid?

A

Supplies blood to outer layers of retina

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29
Q

function of the retina?

A

Has light sensitive rods and cones which enables us to see.

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30
Q

in which segment of the eye is the aqueous humour?

A

Aqueous Humor(AH) in anterior segment

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31
Q

in which segment of the eye is the vitreous humour?

A

Vitreous Humor(VH) in posterior segment

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32
Q

where is the crystalline lend found?

A

Is a transparent, crystalline biconvex structure which is suspended by zonules (suspensory ligaments) from the ciliary body. It can change shape (i.e. become less or more convex.)

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33
Q

what are the two segments of the eye?

A

Anterior segment in front of the lens
Posterior segment behind the lens

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34
Q

what is the anterior segment filled with?

A

Contains a watery fluid called Aqueous Humor

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35
Q

what is the posterior segment filled with?

A

Filled with a gel called Vitreous Humor

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36
Q

what does the aqueous humor help maintain?

A

It helps maintain intraocular pressure.

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37
Q

what does the vitreous humour do?

A

.It helps cushion the retina.

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38
Q

where is the anterior chamber of the eye?

A

Anterior chamber (AC) in front of iris

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39
Q

where is the posterior chamber of the eye?

A

Posterior chamber (PC) behind iris but in front of the lens

40
Q

what is the angle of the anterior chamber?

A

The anterior chamber angle is a part of the eye located between the cornea and iris which contains the trabecular meshwork. The size of this angle is an important determinant of the rate aqueous humour flows out of the eye, and thus, the intraocular pressure.

41
Q

describe the surface anatomy of the eye?

A
42
Q

how many bones is the bony orbit made up of?

A

seven different bones.

43
Q

label the bones of the bony orbit?

A

green - frontal
blue - zygomatic
purple - maxilla
blue - lacrimal
yellow - ethmoid bone
red - sphenoid

44
Q

how many foramen allow neurovascular structures to enter the bony orbit?

A

round foramen just here, called as the optic foramen

45
Q

why are the walls of the orbit quite weak - especially the medial and the inferior walls?

A

surrounding them or adjacent to them are air filled spaces called as the paranasal air sinuses

46
Q

identify the different air sinuses?

A
47
Q

what type of image is this?

A

axial MRI scan

48
Q

what is the anteroposterior length of the eyeball?

A

between 21 and 24 millimetres.

49
Q

what is the anteroposterior length of the entire orbit?

A

40 millimetres

50
Q

what structure is important for support of the eyeball?

A

Orbital fat cushions globe.
Is very important for support.

51
Q

what disease affects fat of the eye?

A

hypertrophies such as in the thyroid
eye disease, which seems to push the eyeball a little more outwards, giving the eye a staring appearance.

This fat is also one of the last reserves of fat that disappear in starvation.
And so when you see people with really sunken eyeballs, you know that they are quite late on in the process of starvation.

52
Q

what are eyelids?

A

skin on the outside, mucous membrane on the inside (conjunctiva)

53
Q

what type of glands do eyelashes have?

A

Eyelashes with sebaceous glands

54
Q

label this diagram?

A
55
Q

what are the conjunctiva?

A

thin vascular membrane that covers inner surface of eyelids and loops back over sclera.

doesn’t cover cornea

56
Q

label the different parts of the conjunctiva?

A
57
Q

what is the lacrimal gland?

A

situated in the orbit laterally. Parasympathetic from Facial nerve. Its ducts open into the conjunctival sac

58
Q

what happens when you blink to tears?

A

During each blink, eyelids spread tears evenly on the surface of cornea

59
Q

where do tears drain through?

A

Tears drain through punctae on the medial side of each eyelid
Drains into lacrimal sac which sits over the lacrimal bone
Then drains through nasolacrimal duct into the inferior meatus of the nasal cavity

60
Q

what are the two types of ocular muscles?

A

Intrinsic muscles
Extrinsic muscles

61
Q

what do intrinsic ocular muscles do?

A

control pupil diameter & helps alter lens curvature to enable us to see near objects

62
Q

what do extrinsic ocular muscles do?

A

(also called extraocular muscles or EOMs)– move the eye.

63
Q

what are the three intrinsic eye muscles?

A

In the iris you have these circular muscles that are arranged just outside of the pupillary edge.
And this is called as the sphincter pupillae or the constrictor pupillae.

You then have the radial muscles in the periphery, and these are called the dilator puplillae.

The other intrinsic muscle you have is present within the ciliary body.
Remember the ciliary body. One of the three structures that form the vascular layer of the eye.
It helps to suspend the lens
Remember the ciliary body. One of the three structures that form the vascular layer of the eye.
It helps to suspend the lens and within the ciliary body, our muscle is called a ciliaris muscle.
And what ciliaris muscle does is that when it contracts it helps to make this lens more convex,
which is what you need to focus, look at something up close.
So once again, that muscle is innervated by parasympathetic and the third nerve.

Therefore, three intrinsic muscles - the ciliaris muscle, constrictor pupillae and the dilator pupillae.

64
Q

what nervous system supplies dilator puplillae?

A

You might remember from the sympathetic and parasympathetic that when you have sympathetic innervation, your pupils dilate.
So the sympathetic supplies the dilator pupillae.

65
Q

what nervous system supplies constrctor puplillae?

A

the parasympathetic, what it does is it constricts the pupil and therefore the parasympathetic supplies the constrictor pupillae.
And this parasympathetic is brought to the pupils through cranial nerve number three or the Oculomotor nerve.

So if you get confused, the two muscles with the ‘C’ are both innervated by the parasympathetic,
which is brought to it by the third cranial nerve.

66
Q

what are the 6 extrinsic ocular muscles that move the eye?

A

4 Straight muscles called recti
Medial rectus (MR)
Lateral rectus (LR)
Inferior rectus (IR)
Superior rectus (SR)

2 oblique muscles
Superior Oblique (SO)
Inferior Oblique (IO)

67
Q

where do the recti muscles arise from?

A

the apex of the orbit from an annular fibrous ring

68
Q

where do the superior oblique muscle arises from?

A

the roof of the orbit posteriorly

69
Q

where do the inferior oblique muscle arise from?

A

the floor of the orbit anteriorly

70
Q

what is the origin and insertion of LPS?

A

Roof of orbit
Upper eyelid

71
Q

where is the origin and insertion of S.O?

A

Lesser wing of sphenoid
Sclera posteriorly

72
Q

where is the origin and insertion of all recti?

A

Tendinous ring
Sclera anteriorly

73
Q

where is the origin and insertion of I.O?

A

Medial part of orbit floor
Sclera posteriorly

74
Q

what nerve supplies SO?

A

Trochlear (IV) nerve supplies muscle with trochlea (SO)

75
Q

what nerve supplies LR?

A

Abducent (VI) nerve supplies muscle which abducts (LR)

76
Q

what muscle supplies everything else?

A

Everything else – Oculomotor (III) nerve.

77
Q

what is the function of the optic nerve(2)?

A

carries visual impulses from the eyeball. Leaves orbit through Optic foramen

78
Q

what is the function of the oculomotor (3) nerve?

A

supplies all the muscles going to the eye except 2 and also supplies levator muscle of the eyelid.
It carries parasympathetic fibres which synapse at the ciliary ganglion in the orbit

79
Q

what is the function of the abducent nerve (IV)?

A

The Abducent (VI) nerve also supplies just one muscle the lateral rectus

80
Q

what is the function of the trochlear nerve?

A

The Trochlear (IV) nerve arises from the dorsal part of the midbrain and supplies 1 muscle the superior oblique

81
Q

what nerves enter into the orbit via the superior orbital fissure?

A

Cranial nerve three (III), four (IV), and six (VI)

82
Q

what does the oculomotor nerve carry?

A

parasympathetic fibres which synapses at the ciliary ganglion before the postganglionic fibres go to innervate the constrictor pupillae and the ciliaris muscle.

83
Q

V1 comes in through the superior orbital fissure what does it supply?

A

general sensation to the upper eyelid and the upper part of the eyeball just there.

84
Q

where does V2 enter into the orbit?

A

inferior orbital fissure

So V1 and V2 also make their way to track into the orbit to supply the orbit and the eyeball with general sensation.

85
Q

what leaves via the infraorbital foramen?

A

tiny branch called the infraorbital nerve leaves to come out through the infraorbital foramen

86
Q

what are the different branches of the ophthalmic division of the trigeminal nerve?

A

Nasociliary nerve
Frontal branch
Lacrimal branch
Maxillary division

87
Q

what is the Lacrimal branch?

A

Smallest branch of the Ophthalmic division, travels laterally and supplies lateral part of orbit and lacrimal gland

88
Q

what is the nasociliary nerve?

A

Small branch of the Ophthalmic division. Goes medially and its branches supply medial part of orbit, ethmoidal air sinus, nasal cavity

89
Q

what is the frontal branch?

A

Largest branch of Ophthalmic division. Divides into supraorbital and supratrochlear branches

90
Q

what is the maxillary division?

A

The maxillary division of trigeminal nerve passes through the inferior orbital canal in the floor of the orbit, and exits through the infraorbital foramen as the infraorbital nerve

91
Q

what is the opthalmic artery?

A

The Ophthalmic artery is a large branch of the Internal Carotid artery. It supplies all structures in the orbit, and also some branches to the nasal cavity and forehead.

92
Q

describe the arterial supply of the face?

A

You’ve got the common carotid artery that at the upper border of the thyroid cartilage is going to divide into the external carotid and the internal carotid arteries.

The external carotid supplies most of the face while the internal carotid gives off no branches in the neck,
it enters into the cranial cavity through the foramen lacerum and the carotid canal.
Once inside it supplies most of the structures inside the cranial cavity, the brain
by way of dividing into three major branches, the anterior, the middle and the posterior cerebral arteries.

One of the first branches of the internal carotid arteries however, is the ophthalmic artery.
And this artery goes to supply all of the orbit and its contents.

93
Q

describe the Ophthalmic artery and its branches??

A
  1. Central retinal artery that travels within the substance of the optic nerve, supplies inner layers of the retina
    3,4,5. Short posterior ciliary arteries that supply the posterior part of the choroid (and outer retina
  2. Long posterior ciliary arteries that supply the anterior choroid, ciliary body, iris

7,8. Anterior and posterior ethmoidal arteries

  1. Muscular arteries
94
Q
A
95
Q

describe the venous drainage of the eye?

A

Superior and inferior ophthalmic veins which drain into the cavernous sinus

96
Q

what does this image show?

A

Cavernous sinus

97
Q

what are the contents of the cavernous sinus?

A

sphenoid bone with the sphenoid air sinus.
There’s the sella turcica or the pituitary fossa with the pituitary gland sitting in it.
with the superior ophthalmic vein and sometimes the inferior ophthalmic vein coming back.
And just there on the side of that is where you’d have the cavernous sinus.
So there’s your cavernous sinus on one side. There it is on the other side.
It’s made up of between layers of dura mater. It is lined with endothelium.
And you’ve got blood flowing inside of this cavernous sinus.
The importance the cavernous sinus has clinically, lies in the fact that these cranial nerves that have to go into the orbit
through the superior ophthalmic, superior orbital fissure, have to all pass through the walls of the cavernous sinus.

So you can see here that’s your trigeminal ganglion, a wee one.
You can see cranial nerves three, four and six. And you can even see the loop of the internal carotid artery is sitting within this cavernous
You have to understand that these structures, while inside the sinus, are separated from that venous blood by a layer of epithelium.

So it’s not as if this artery and the nerves are bathed in the venous blood,
they’re separated from it by endothelium. Nevertheless, this is a bit of a recipe for disaster because you could have a fistula developing just here,
which then means the orbit does not get enough blood supply.
You could have infection of these sinuses, which means venous drainage from the orbit
is impeded and all these structu
e structures sitting here get affected as well.

The cavernous sinus is of clinical importance and we’ll deal with it again when we’re looking at intracranial venous sinuses.
But remember that it’s important because blood from the orbit drains into it
And all these nerves and the artery are situated within the cavernous sinus

Head and Neck (15 decks)

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